Calling the investigations "highly complex", Salzburg prosecutors said that all four are believed to belong to the so-called Islamic State extremist group, which claimed responsibility for the Paris attacks.
The officials said that in addition to an Algerian and a Pakistani, whose arrest on December 10 was announced several days later, two others have been detained since December 18.
The first two, aged 28 and 34, were believed to have been in the same migrant boat travelling to Greece as two men involved in the Paris atrocities that killed 130 people, prosecutors said in a statement.
They then arrived in Salzburg in western Austria at the end of November - after the Paris killings - and Austrian police arrested them at a centre for migrants on December 10.
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Eight days later, the other two, a 25-year-old Moroccan and a 40-year-old Algerian, were arrested "because of indications of close contact with both the first two suspects," prosecutors said.
The statement stressed that contrary to some media reports, the men had not confessed to planning any attacks.
There is however no evidence that these two were involved in any attacks in Europe, nor of any links to the other four men detained, prosecutors said, although investigations were continuing.